1. Field of the Invention
The present invention relates to an image forming apparatus such as a printer, a copying machine and a facsimile which adjusts and controls a density correction, a registration deviation correction, a forcible consumption of toner or the like.
2. Description of the Related Art
In an image forming apparatus such as a printer, a copying machine and a facsimile, a toner image density and a registration deviation is corrected. In such correction, a pattern image (toner image) for measurement is formed on a photosensitive member or an intermediate transfer member, and the density and the position of this pattern image are detected. On the basis of the detected result, these corrections are made.
As such a detection method, conventionally, a method referred to as “patch check ATR (Auto Toner Replenishment” has been employed. In this patch check ATR, the pattern image is formed on the photosensitive member or the intermediate transfer member with toner and irradiated with light. The reflected light is read by a light detection unit such as a photodiode. Then, on the basis of the result of the reading, a toner replenishing unit is operated so as to maintain a toner density of a developer constant in a developing apparatus. This patch check ATR is a toner density detection method which utilizes characteristics of the toner. That is, optical properties of the toner image obtained by developing an electrostatic latent image depend on the toner density of the developer under a certain fixed electrostatic latent image condition.
Japanese Patent Application Laid-Open No. H5-333699 discusses adjustment control of a toner density correction. According to this document, a toner density of a developer in a developing apparatus and accordingly, a final image density is maintained constant. Further, Japanese Patent Application Laid-Open No. H6-51607 discusses adjustment control of a registration deviation correction. Japanese Patent Application Laid-Open No. H9-34243 discusses an example other than the above described type in which a pattern image is formed for adjustment control (adjusting toner image) without transferring to a recording material. This document describes the control under which toner is forcibly consumed to prevent a decrease in density and degradation of granularity in a low density part when an image having small toner consumption is continuously outputted. This control employs a method in which toner is forcibly consumed, and a high density toner image is formed on a photosensitive member or an intermediate transfer member. The used toner is disposed of into a waste toner containing unit or the like.
As timing for executing the adjustment control described above, there are various cases according to the purpose or the use of the adjustment such as at the time of turning the power of an image forming apparatus on, at the time of staring image forming, between sheet feeding (between recording materials) during continuous image forming, and at the time of completing the image forming. Generally, the more the adjustment control described above is executed, the more constant the toner density can be maintained. However, on the other hand, there are possibilities that printout time of a first sheet of the image forming apparatus is delayed or the throughput (productivity) is decreased.
In particular, when this adjustment control is executed between sheet feeding during continuous image forming, the number of recording materials on which the image is formed within a fixed time decreases. This effect is remarkable when the image is continuously formed on a large number of recording materials. That is, downtime accompanied with the adjustment control significantly lowers productivity and reduces usability. Therefore, there is a method in which, the adjustment control of the density is not executed when a density deviation is within a designed allowable range and a higher priority is given to the usability. In this method, only at predetermined timing, the adjustment control of the density is executed. In this case, when the predetermined timing is set directly before the density deviation exceeds the allowable range, a decrease in usability can mostly be prevented.
Adjustment control of the toner density correction, the registration deviation correction, and the forcible toner consumption is respectively essential control to perform stabilization of the image density, prevention of the position deviation and stabilization of granularity in the low density part, and further reduction in downtime has been required.
Among such methods, for the purpose of reducing downtime, there are also methods such as devising a shape of the pattern image, reducing an implementation frequency of the adjustment control between sheets. However, the downtime of the adjustment control is by no means eliminated.
On the other hand, according to a method discussed in Japanese Patent Application Laid-Open Nos. H10-31375 and H5-188783, a pattern image is formed on a non-sheet passing section (non-image forming section) parallel with a recording material conveyance area and an apparatus is adjusted in real time. That is, according to Japanese Patent Application Laid-Open No. H10-31375, the pattern image for detecting a density formed on the non-sheet passing section parallel with the recording material conveyance area is formed on the non-sheet passing section located at the end of a transfer roller. Density control is executed on the basis of the detected result of this pattern image. Further, according to Japanese Patent Application Laid-Open No. H5-188783, the pattern image for detecting a density is formed on the non-sheet passing section in a photosensitive member parallel with image forming. Density detection control and density correction control according to the detected result are executed simultaneously with the image forming.
However, if a configuration disclosed in Japanese Patent Application Laid-Open Nos. H10-31375 and H5-188783 is employed, when an image is formed on a recording material having a maximum sheet passing width, a space for forming the pattern image is required further outside the sheet passing width. Further, a deviation normally occurs within a tolerance in the sheet passing area. When the tolerance is taken into consideration, the pattern image has to be formed apart from a maximum sheet passing area at a predetermined interval. As a result, an apparatus becomes larger-sized. Such an increase of size in a direction of the sheet passing width causes a significant problem particularly in a low-speed and a medium-speed machines for which compactness is an important subject.
As described above, if a conveyance interval of the recording material is widened and the pattern image for the adjustment control is formed on an interval between sheets provided in a recording material conveyance direction, the downtime increases and the throughput reduces. On the other hand, if the pattern image for the adjustment control is formed outside the maximum sheet passing width and the pattern image is formed in a position parallel with the toner image that is to be formed on the recording material, reduction in throughput can be prevented. However, a size of the apparatus in a direction of the sheet passing width of the image forming apparatus increases.